High bandwidth modulation and transmission

ABSTRACT

This disclosure relates systems and methods for a high bandwidth modulation and transmission of communication signals.

BACKGROUND

A modulator is arranged in a device for signal transmission, such asused in systems for wireless or wireline communication. One of thefunctions of a modulator is to modulate a useful signal representing aninformation to be transmitted onto a carrier frequency signal so toprovide a transmission signal. The transmission signal is amplifiedbefore being provided to a transmission channel. In case of abase-station of a mobile communication system, the amplifier has toprovide for a high amplification gain.

Generally, in mobile communication systems, diverse modulation schemesallowing for a high bandwidth are provided, such as EDGE (Enhanced DataRates for GSM Evolution), UMTS (Universal Mobile TelecommunicationSystem), etc. These modulation schemes usually provide a non-constantenvelope of the transmission signal. This may be due to an amplitudemodulation of the transmission signal. The amplitude modulation carriespart of the information transmitted. To allow for a correct demodulationand reassembly of the information, certain linearity requirements haveto be fulfilled by the modulator. E.g., the linearity requirements areset by a standard specification. In consequence, the power amplifier ofa base-station has to provide a linear amplification over a wide rangeof signal level. This is usually achieved by providing for a“quasi-linear” amplifier running with a high back-off to ascertain thelinearity requirements with respect to the transmission signal. Thismode of operation leads to a low efficiency in power and usually tohigher costs in production of an according modulator.

For these and other reasons, there is a need for the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Thesame numbers are used throughout the drawings to reference like featuresand components.

FIG. 1 is a block diagram illustrating an exemplary transmission device.

FIG. 2 is a block diagram illustrating an exemplary transmission device.

FIG. 3 is a block diagram illustrating an exemplary modulator.

FIG. 4 is a block diagram illustrating an exemplary IQ-modulator.

FIG. 5 is a signal diagram illustrating exemplary signals in relation toa Pulse-Width-Modulator (PWM).

FIG. 6 is a signal diagram illustrating exemplary frequency spectrum ofsignals in relation to a PWM.

FIG. 7 is a signal diagram illustrating exemplary frequency spectrum ofsignals in relation to a PWM.

FIG. 8 is a signal diagram illustrating exemplary Signal-to-Noise-Ratio(SNR) of an Envelope Modulator.

FIG. 9 is a signal diagram illustrating exemplary frequency spectrum ofsignals in relation to a up-conversion mixer.

FIG. 10 is a signal diagram illustrating exemplary frequency spectrum ofsignals in relation to a up-conversion mixer.

FIG. 11 is a signal diagram illustrating exemplary frequency spectrum ofsignals in relation to an up-conversion mixer.

FIG. 12 is a signal diagram illustrating exemplary frequency spectrum ofsignals in relation to an up-conversion mixer.

FIG. 13 is a schematic diagram of a technique to reduce mirrorfrequencies by a baseband-based modulation.

FIG. 14 illustrates an exemplary method for modulating a useful signalinto a modulated signal.

DETAILED DESCRIPTION

This disclosure is directed to techniques for modulation in atransmission device. More particularly, the techniques involveimplementation of a transmission device and of a modulator. Thedisclosed apparatus' can be implemented in a variety of communicationdevices or systems. For example, a transmission device or a modulatorcan be implemented in mobile phones, base stations, etc. The followingsystems and methods are described with reference to a mobilecommunication system; however, it will be appreciated that the disclosedtransmission devices and modulators can be implemented generally in anyelectronic communication system.

Mobile communication systems include components such as mobilecommunication devices, base stations, etc., that can receive inputsignals . . . .

The disclosed technique for implementing a modulation involves acombination of a switched output stage and an error estimation path.

Exemplary Systems

FIG. 1 illustrates an exemplary transmission device 100. The order inwhich the blocks of the system are described, is not intended to beconstrued as a limitation, and any number of the described system blockscan be combined in any order to implement the system, or an alternatesystem. Additionally, individual blocks may be deleted from the systemwithout departing from the spirit and scope of the subject matterdescribed herein. Furthermore, the system can be implemented in anysuitable hardware, software, firmware, or a combination thereof, withoutdeparting from the scope of the invention.

The transmission device includes an input 102. A baseband signalcomprised of information to be transmitted may be received at the input102. The baseband signal is passed to a Modulation Path 104. TheModulation Path 104 performs a modulation of the baseband signal toproduce an output signal. A modulation may include any of the followingsignal processing: coding; up-converting the baseband signal on acarrier signal; amplifying; filtering; etc. The different kind of signalprocessing may be performed at various sequence or times.

The Modulation Path 104 includes one or several switched output stagesnot shown in FIG. 1. A switched output stage may be a switchedamplifier, i.e. an amplifier of any of Class-F; Inverse Class F; ClassD, Class S, etc. In an ideal switched amplifier, current and voltage arenot present at the same time. In consequence, high power efficiency isachieved.

To achieve an according bandwidth, the Modulation Path 100 may include aplurality of switched output stages in parallel. In another embodiment,it may include a single switched output stage. In one embodiment, itincludes at least one serial circuit of switched output stages toachieve a required power level of the output signal.

In one embodiment, the Modulation Path 104 further includes a codingunit that performs a coding the time depending phase component and thetime depending envelope component of the input signal received at input102. The coding unit may thus be arranged to provide a high bandwidthmodulation scheme, such as 8-PSK, used in EDGE, UMTS, etc. Oneelementary function of the coding unit is to provide a rectangular pulsetrain derived from the baseband signal provided at the input 102.Exemplary implementations of the coding unit make use of a Delta-SigmaModulation, Pulse-Width Modulation or any other method to transform anenvelope signal into pulses. One aspect of using a coding unit is thatthe spectrum of the rectangular pulse train concentrates at multiples ofthe reference frequency used in the coding unit. Thereby, gaps in thespectrum may be used to improve the SNR in the high frequency domain,e.g. after up-converting the rectangular pulse train on a carrierfrequency. Another aspect is that the frequency of switching at theoutput stage is reduced in comparison to a known band-pass modulator.Thus, a high efficiency is achieved while spectral componentsconcentrate around the carrier frequency, which implies a smallerbandwidth of the output stage needed.

The transmission device 100 further includes an Error Computation Unit106. The function of the Error Computation Unit 106 is to estimate anaccording Inband Error of the output signal produced by the ModulationPath 104. This is achieved by producing an error signal based oninformation on error contributions, such as unwanted image components,quantization effects, non-linearity present in the output signalprovided by the Modulation Path 104. Information on error contributionsmay be retrieved by a feedback or feed forward kind of correction, i.e.by using at least one of:

-   -   a copy of the output signal, such as a down-converted version of        the signal provided by the switched output stage;    -   a copy of the rectangular pulse train produced by the coding        unit;    -   a copy of the baseband signal; etc.        Estimation of the Inband Error may be performed in either the        digital or the analogue baseband section of the transmission        device 100.

The Error computation unit 106 includes a linear output stage not shownin FIG. 1. A linear output stage may be a linear amplifier, i.e. anamplifier of any of Class-A; Class B, Class AB, etc. In consequence, asimple output stage implementation may be used. Since the power levelInband Error of Modulation Path 104 will generally be much smaller thanthe power level of the Inband part of the output signal produced byModulation Path 104, a linear amplifier is sufficiently reliable totransfer the signal representing the Inband Error on a necessary powerlevel.

The transmission device 100 further includes an Error Correction Unit108. The Error Correction Unit 108 receives the output signal providedby the Modulation Path 104 and the error signal provided by the ErrorComputation Unit 106. Its function is to correct the output signal bythe error signal to produce a transmission signal. The Error CorrectionUnit 108 may include any of the following apparatus': an adder; a powercombiner; a filter, such as a band-pass filter, etc. The transmissionsignal is provided at an output 110 comprised by the transmission device100. The output 110 may couple to a feed to feeds the transmissionsignal into a transmission channel, such as an antenna or a plug.

FIG. 2 illustrates an exemplary system including a modulator formodulating a useful signal into a modulated signal. The system 200 maybe arranged in an RF (radio frequency) transmission section of abase-station. The system 200 receives an input signal or incomingdata-stream 102. The input signal 102 may correspond to baseband signal,as described with respect to FIG. 1. The input signal 102 is passed to aCoding Unit 202.

The Coding Unit 202 performs a coding the time depending phase componentand the time depending envelope component of the input signal 102. TheCoding Unit 202 may thus be arranged to provide a high bandwidthmodulation scheme, such as 8-PSK, used in EDGE, UMTS, etc. Oneelementary function of the Coding Unit 202 is to provide a pulse trainderived from the input signal 102. Exemplary implementations of theCoding Unit 202 make use of a Delta-Sigma Modulation or of a Pulse-WidthModulation or any other method to transform an envelope signal intopulses. In general, the Coding Unit 202 produces a first intermediatesignal 204, being a rectangular pulse train.

An Up-Converter 206 receives the first intermediate signal 204. Itfurther receives a carrier signal 208, i.e. a high frequency signal. TheUp-Converter 206 performs an up-conversion of the first intermediatesignal 204 by the carrier signal 208 to produce a second intermediatesignal 210. This corresponds to shifting the center frequency of thefirst intermediate signal 204, i.e. baseband, to the center frequency ofthe carrier signal 208, i.e. the carrier frequency.

In many communication systems, the carrier frequency is more than 1 GHz.Yet, in other communication systems, the carrier frequency may be lowerthan 1 GHz, e.g. in GSM it is 800-900 MHz.

The Up-Converter 206 may include a mixing device, such as a multiplier.A local oscillator, not shown in FIG. 2, may provide the carrier signal208. It may be phase modulated by a phase modulator, to include part ofthe information to be transmitted.

A Switched Output Stage 212 receives the second intermediate signal 210.It performs an amplification of the second intermediate signal 210 toprovide an output signal 214. The Switched Output Stage 212 may includea switched amplifier, i.e. an amplifier of any of Class-F; Inverse ClassF; Class D, Class S, etc. To achieve an according bandwidth/outputpower,Switched Output Stage 212 may include a plurality of switched amplifiersin parallel. In another embodiment, it may include a single switchedamplifier. In one embodiment, it includes at least one serial circuit ofswitched amplifiers to achieve a required power level of the outputsignal 214.

The system 200 further includes an Error Estimator 216. The ErrorEstimator 216 estimates an Inband Error of the output signal 214. Thisis achieved by producing an error signal based on information on errorcontributions, such as unwanted image components, quantization effects,non-linearity present in the output signal 214. Information on errorcontributions may be retrieved by a feedback or feed forward kind ofcorrection, i.e. by using at least one of:

-   -   a copy or derivative of the output signal 214, such as a        down-converted version of the signal provided by the switched        output stage 212;    -   a copy or derivative of the first intermediate signal 204;    -   a copy or derivative of the second intermediate signal 210;    -   a copy or derivative of the input signal 102; etc.        Estimation of the Inband Error may be performed in either the        digital or the analogue baseband section of the system 200. The        Error Estimator 216 provides a first intermediate error signal        218 based on the estimated Inband Error.

A second Up-Converter 220 receives the first intermediate error signal218. It further receives a second carrier signal 222, i.e. a highfrequency signal. The second carrier signal 222 may be identical to thecarrier signal 208. The second Up-Converter 220 may be of a structuresimilar to Up-Converter 206. It performs an up-conversion of the firstintermediate error signal 218 by the carrier signal 222 to produce asecond intermediate error signal 224. This corresponds to shifting thecenter frequency of the first intermediate error signal 218, e.gbaseband, to the center frequency of the carrier signal 222, i.e. thecarrier frequency.

A Linear Output Stage 226 receives the second intermediate error signal224. It performs an amplification of the second intermediate errorsignal 224 to provide an error signal 228. It includes a linearamplifier, such as a Class A, Class B, Class AB, etc. The inventors haverecognized that the dynamic range of the error signal 228 is muchsmaller than the dynamic range of the output signal 214. It is thereforesufficient to perform amplification of the error signal by a simplelinear amplification structure.

The system 200 further includes a Combiner 230. The Combiner 230receives the output signal 214 and the error signal 228. It performs acombination of the output signal 214 and the error signal to provide atransmission signal 232. This may be achieved by subtracting or addingthe error signal 228 to the output signal 214. The Combiner 230 may alsoperform a band-pass filtering of the result of combination. Thetransmission signal 232 may be transferred to a transmission channel bymeans of an according feed, such as an antenna or a plug.

The Coding Unit 202, the Up-Converter 206, and the Switched Output stage212 form a Modulation Path that provides the output signal 214, derivedfrom input signal 102 by a modulation of the later. The modulation ofthe input signal 102 is performed by making use of a switchedamplification. There is a large variety of coding an enevelope sectionand/or a phase section of a baseband signal to achieve an accordinginput to the switched amplifier. This includes techniques, such as anEnvelope Modulation, which is described in further detail with respectto FIG. 3, or as a Cartesian Modulation, resp. an IQ-Modulation, whichis described in further detail with respect to FIG. 4.

FIG. 3 illustrates an exemplary system including a modulator formodulating a useful signal into a modulated signal. The system 300 makesuse of an Envelope Modulation. The system 300 receives an input signalor incoming data-stream. The input signal may correspond to basebandsignal, as described with respect to FIG. 1. The input signal includes afirst input signal 302 representing an envelope component of the inputsignal. It further includes a second input signal 304 representing aphase component of the input signal.

A Pulse Width Modulator (PWM) 306 receives the first input signal 302.It performs a coding of the first input signal 302 to a rectangularpulse stream. The PMW 306 operates at a reference frequency chosen withregard to the bandwidth of the envelope component and to the requiredSNR. It produces a first intermediate signal 204 in form of a pulsestream. The width of a pulse is in linear relation to a value of anamplitude at a sampling time determined by the reference frequency.

A Phase Modulator 308 receives the second input signal 304. The PhaseModulator 308 provides a high-frequency and phase modulated LO signal310 having a center frequency at a carrier frequency of the system 300.It may include any structure of a frequency synthesizer, such as aDigitally Controlled Oscillator (DCO), a Voltage Controlled Oscillator(VCO); a Phase-Locked Loop (PLL), a Digital PLL (DPLL), a RingOscillator; etc. The LO signal 310 thus carries the phase information ofthe input signal, shifted to the carrier frequency. In many embodiments,the LO signal 310 is a rectangular (bit-like) pulse stream.

A First Mixer 312 receives the first intermediate signal 204 and the LOsignal 310. It mixes or performs of a multiplication of the two toprovide a second intermediate signal 210. In real implementation, a knotmay replace the First Mixer 312. A Switched Output Stage 212, asdescribed with respect to FIG. 2 receives the second intermediate signal210 to provide an output signal 214.

A Filter 314 receives the first intermediate signal 204. It performs afiltering of the first intermediate signal 204 to estimate an InbandError. The Filter 314 may include a highpass type of filter. It providesa first intermediate error signal 218.

A Second Mixer 316 receives the first intermediate error signal 218 andthe LO signal 310. It mixes or performs of a multiplication of the twoto provide a second intermediate error signal 224. In realimplementation, a knot may replace the Second Mixer 316. A Linear OutputStage 226, as described with respect to FIG. 2 receives the secondintermediate error signal 226 to provide an error signal 228.

An Adder/Power-Combiner 318 receives the output signal 214 and the errorsignal 228. It subtracts the error signal 228 from the output signal214. The resulting signal is passed to a Band-Pass Filter (BPF) 320. TheBPF 320 performs a band-pass filtering to provide a transmission signal112. The transmission signal 232 may be transferred to a transmissionchannel by means of an according feed, such as an antenna or a plug.

FIG. 4 illustrates an exemplary system including a modulator formodulating a useful signal into a modulated signal. The system 400 makesuse of an IQ Modulation. The system 400 receives an input signal orincoming data-stream. The input signal may correspond to basebandsignal, as described with respect to FIG. 1. The input signal includes afirst input signal 402 representing an Inphase component (I) of theinput signal. It further includes a second input signal 404 representinga Quadrature component (Q) of the input signal.

A First PWM 406 receives the first input signal 402. It performs acoding of the first input signal 402 to a rectangular pulse stream. TheFirst PMW 406 operates at a reference frequency chosen with regard tothe signal bandwidth and to the required SNR. It produces a firstintermediate signal 408 in form of a rectangular pulse stream. Since theInphase component takes positive, as well as negative values, a 3 levelpulse-width modulation may be applied. A pulse thus may take one of thevalues (+A, 0, −A), A being the maximal amplitude of the rectangularpulse stream. Transition from +A to −A may always pass through 0 toavoid phase shifts by 180° (i.e. by Pi). The width of a pulse is inlinear relation to a value of amplitude of the first input signal 402 ata sampling time determined by the reference frequency.

A Second PWM 410 receives the second input signal 404. It performs acoding of the second input signal 404 to a rectangular pulse stream. TheSecond PMW 408 operates at same reference frequency as the First PWM406. It produces a second intermediate signal 412 in form of arectangular pulse stream. Since the Quadrature component takes positive,as well as negative values, a 3 level pulse-width modulation may beapplied. A pulse thus may take one of the values (+A, 0, −A), A beingthe maximal amplitude of the rectangular pulse stream. Transition from+A to −A may always pass through 0 to avoid phase shifts by 180° (i.e.by Pi). The width of a pulse is in linear relation to a value ofamplitude of the second input signal 404 at a sampling time determinedby the reference frequency.

A First Mixer 414 receives the first intermediate signal 408 and a LOsignal 416. It mixes or performs of a multiplication of the two toprovide a third intermediate signal 418. In real implementation, a knotmay replace the First Mixer 414. The LO signal 416 may be provided by afrequency synthesizer or Local Oscillator, such as, such as a DigitallyControlled Oscillator (DCO), a Voltage Controlled Oscillator (VCO); aPhase-Locked Loop (PLL), a Digital PLL (DPLL), a Ring Oscillator; etc. AFirst Switched output stage 420, as described with respect to FIG. 2receives the third intermediate signal 418 to provide an Inphase outputsignal 422.

A Second Mixer 424 receives the first intermediate signal 412 and aphase-shifted LO signal 426. It mixes or performs of a multiplication ofthe two to provide a fourth intermediate signal 428. In realimplementation, a knot may replace the Second Mixer 424. Thephase-shifted LO signal 426 corresponds to the LO signal 416 by aphase-shift of 90° (i.e. Pi/2). The phase shifted LO signal 426 may bederived from the LO signal 416, e.g by a phase shifting device, a delayline, etc. A frequency synthesizer, the same or a different to thefrequency synthesizer that generates LO signal 416 may generate thephase-shifted LO signal 426. A Second Switched Output Stage 430, asdescribed with respect to FIG. 2 receives the fourth intermediate signal428 to provide an Quadrature output signal 432.

The signal paths including the First Mixer 414, the First SwitchedOutput Stage 420, the second Mixer 424 and the Second Switched OutputStage 430 form an IQ-Modulation Path.

A First Filter 434 receives the first intermediate signal 408. Itperforms a filtering of the first intermediate signal 408 to estimate anInphase component of an Inband Error. The First Filter 434 may include ahighpass type of filter. It provides a first intermediate error signal436. A Second Filter 438 receives the second intermediate signal 412. Itperforms a filtering of the second intermediate signal 412 to estimatean Quadrature component of an Inband Error. The Second Filter 438 mayinclude a highpass type of filter. It provides a second intermediateerror signal 440.

A Third Mixer 442 receives the first intermediate error signal 436 andthe LO signal 416. It mixes or performs of a multiplication of the twoto provide a third intermediate error signal 444. A Fourth Mixer 446receives the second intermediate error signal 440 and the phase-shiftedLO signal 426. It mixes or performs of a multiplication of the two toprovide a fourth intermediate error signal 448. An Adder 450 receivesthe third intermediate error signal 444 and the fourth intermediateerror signal 448 to provide a combined error signal 452. A Linear OutputStage 226, as described with respect to FIG. 2 receives the combinederror signal 452 to provide an error signal 228.

The system 400 further includes a combiner 454 that receives the Inphaseoutput signal 422 and the Quadrature output signal 432 to perform aphase-correct combination of both. It further receives the error signalto subtract the Inband Error contribution. It thus provides atransmission signal 456 that may be passed via a BPF to a transmissionchannel, e.g. by means of a plug or an antenna.

In general, any high-frequency signal may be written in the subsequentrepresentation, if being phase- and amplitude-modulated:x(t)=a(t)cos(ω_(c) t+φ(t)).  (1)The amplitude a(t) of the signal depends on time t, like the phase φ(t)is time-depending. Time-dependency of both components is used to codeinformation on the signal. The carrier frequency f_(c) is considered byω^(c)=2*Pi*f_(c). Because of the time-dependancy of the amplitude a(t),this signal may not be used for controlling a switched amplifier. In thedescribed technique, the envelope contribution a(t) is coded, e.g. usinga pulse-width modulation.

The resulting coded signal is a rectangular pulse signal having aconstant frequency, which depends on the reference frequency of theapplied coding, such as delta-sigma coding, pulse-width modulation, etc.In pulse-width modulation, the pulse length is in linear dependency ofthe amplitude a(t). The reference frequency is chosen in dependency ofbandwidth of the envelope contribution, i.e. the amplitude. It will alsobe chosen with respect to a required SNR: In general, it is smaller thana frequency used in known techniques, such as a Band-pass Modulation.The time domain of an envelope signal modulated by a pulse-widthmodulation is shown in FIG. 5, FIG. 6, and FIG. 7. The signal diagramsshow exemplary values of signals that vary for different systems. Theyare but an exemplary illustration of the effect of the describedtechnique.

FIG. 5 is a signal diagram 500 illustrating exemplary signals inrelation to a Pulse-Width-Modulator (PWM). On the abscissa 501, a shorttime interval of 3*10⁻⁸s is shown. On the ordinate 502, a normalizedmagnitude of an envelope signal 503 and of a respective PWM signal 504are depicted.

FIG. 6 and FIG. 7 are signal diagrams 600 and 700 illustrating thespectrum of exemplary signals in relation to a Pulse-Width-Modulator(PWM). The abscissa 601 shows a frequency domain [−9*10¹⁰ Hz, 9*10¹⁰Hz]. On the ordinate 602 a Power Spectrum Density in the domain [−160dB/Hz, −60 dB/Hz] of a baseband signal 603, an envelope signal 604 and aPWM modulated envelope signal 605 are depicted. Signal digram 700 showsa different frequency domain [−1.5*10⁹ Hz, 1.5*10⁹ Hz] on abscissa 701for the same system as used with respect to diagram 600. Ordinate 702scales on a domain [−170 dB/Hz, −50 dB/Hz].

Usually, a pulse-width modulated signal has a larger bandwidth than thecarrier frequency signal. In consequence, the spectral parts of abaseband signal overlap, if up-converted by a carrier frequency f_(c).

In some embodiments, a modulation frequency f_(PWM) of some pulse-widthmodulated signals in a systems using the described technique is adjustedaccording to the following relation:f _(PWM)*(n−0.5)=2*f _(c),  (2)n being an integer number. This results in a maximal SNR, in relation ofthe complex baseband signal a(t)*ej*φ(t) to noise caused by imagefrequency.

FIG. 8 is a signal diagram 800 illustrating exemplarySignal-to-Noise-Ratio (SNR) of an Envelope Modulator. Abcissa 801 showsa frequency domain [−1.5*10⁹ Hz, 1.5*10⁹ Hz] of a modulation frequencyf_(PWM) Ordinate 802 shows a domain of the SNR [0 dB, 80 dB]. Thediagram shows a strong dependency of the SNR with respect to themodulation frequency f_(PWM). A reason might be that spectral componentsconcentrating around multiples of the modulation frequency f_(PWM) getwider with higher frequency, so that they eventually overlap and bandgaps get rare with high frequency. This effect is shown in FIGS. 9 and10 exemplary frequency spectrums of signals in relation to aup-conversion mixer. FIG. 9 shows a Power Spectrum Density of modulationfrequency f_(PWM) at 500 MHz up-converted at different carrier frequencyf_(c). This corresponds to a SNR of approx. 70 dB. FIG. 10 shows a PowerSpectrum Density of modulation frequency f_(PWM) at 290 MHz up-convertedat different carrier frequency f_(c). Since a lower modulation frequencyf_(PWM) is chosen, spectral band gaps grow as compared to FIG. 9. TheSNR is at approx. 43 dB, i.e. reduced as to a modulation frequencyf_(PWM) at 500 MHz.

The described technique makes use of further reducing the SNRrequirements. Mirror contributions of the PWM modulated signal at±2*f_(c) are extracted, e.g. by high pass or bandpass filtering. Themirror contributions a mixed (e.g. by multiplication) with a phasemodulated carrier signal to the desired carrier frequency f_(c). Thespectrum of such a signal is shown in FIGS. 11 and 12.

As shown in FIGS. 11 and 12 power density of mirror contributions at±2*f_(c) is much smaller than components at the signal band around thecarrier frequency f_(c). The mirror contributions a re amplified using alinear amplification, since smaller efficiency of a linear amplificationin comparison to a switched amplification does not give rise to anymajor disadvantage. In contrast, a simple architecture of an amplifiermay be used.

FIG. 13 shows a schematic diagram of a technique to reduce mirrorfrequencies by a baseband-based modulation. In a first graph, a spectrumof a PWM modulated signal is depicted, having desired basebandinformation 1301 and unwanted mirror contributions 1302 and 1303. In asecond graph, the spectrum is shown after up-conversion to a carrierfrequency f_(c). It is shown that mirror contributions move into thesignal band. A third graph shows how mirror contributions 1302 and 1303are transferred to the carrier frequency f_(c) in an error estimationunit. These shifted mirror contributions 1302 and 1303 are used tocancel unwanted signals of the second graph.

It has to be noted that mirror components are deterministic. Mirrorcontributions depend on the envelope, the modulation frequency f_(PWM)used for PWM modulation, the modulation method, etc. The contributionsmay therefore e calculated be means of a digital signal processorinstead of using a filter as shown with respect to the above-describedexamples.

Exemplary Method

FIG. 14 illustrates an exemplary method 1400 for modulating a usefulsignal into a modulated signal. The order, in which the method isdescribed, is not intended to be construed as a limitation, and anynumber of the described method blocks can be combined in any order toimplement the method, or alternate method. Additionally, individualblocks may be deleted from the method without departing from the spiritand scope of the subject matter described herein.

The method introduced may, but need not, be implemented at leastpartially in architecture(s) such as shown in FIGS. 1-4. In addition, itis to be appreciated, that certain acts in the methods need not beperformed in the order described, may be modified, and/or may be omittedentirely. Furthermore, the method can be implemented in any suitablehardware, software, firmware, or a combination thereof, withoutdeparting from the scope of the invention.

At block 1402, a useful signal is received as input. The useful signalmay comprise information to be transmitted, such as audio, video, mail,etc. At block 1404, the useful signal is coded to provide a firstintermediate signal. Coding may be based on a methods such asSigma-Delta Modulation or Pulse Width Modulation. At block 1406, thefirst intermediate signal is up-converted to provide a secondintermediate signal. Up-converting refers to any shifting of centerfrequency of a spectrum. It is performed using a RF carrier signal, suchas a carrier signal of a wireline or wireless communication system. TheRF carrier signal may comprise a single carrier frequency or a frequencyband. At block 1408, the second intermediate signal is amplified.Amplification may involve a switched amplification, thereby achieving ahigh efficiency. An output signal is provided.

At block 1410, a first intermediate error signal is provided. The firstintermediate error signal may be derived from the first intermediatesignal, e.g. involving a step of filtering. Since error contributionsare deterministic, the first intermediate error signal may be providedby other means, such as a digital signal processing. At block 1412, thefirst intermediate error signal is up-converted to provide a secondintermediate error signal. As above, up-converting refers to anyshifting of center frequency of a spectrum. It is performed by using theRF carrier signal. At block 1414, the second intermediate error signalis amplified. Amplification may involve a linear amplification, therebymaking use of a simple implementation. An error signal is provided.

At block 1416, a output signal and the error signal are combined toprovide a modulated signal. This step may include a bandpass filteringof the modulated signal.

CONCLUSION

Although embodiments for power amplifier with output power control havebeen described in language specific to structural features and/ormethods, it is to be understood that the appended claims are notnecessarily limited to the specific features or methods described.Rather, the specific features and methods are disclosed as exemplaryimplementations for power amplifier with output power control.

1. A transmission device comprising: a first path that receives a firstsignal comprising useful information and that provides a pulse streamsignal, the first path having a switched-mode output stage; a secondpath that receives a second signal and that provides a phase modulatedsignal; a mixer that receives the pulse stream signal and the phasemodulated signal and provides an intermediate signal to theswitched-mode output stage; an error computation unit that provides anerror signal representative of an Inband Signal Error of the pulsestream signal, the error computation unit having a linear output stage,the error computation unit including a filter coupled to a second mixer,the filter to provide the Inband Signal Error to the second mixer, andthe second mixer to perform an operation on the Inband Signal Error andthe phase modulated signal to provide the error signal; and an errorcorrection unit that receives the intermediate signal and the errorsignal and that provides a transmission signal.
 2. A transmission deviceaccording to claim 1, the first path to perform an amplitude modulation.3. A transmission device according to claim 2, the linear output stagebeing arranged downstream of the error computation unit.
 4. Atransmission device according to claim 1, the error correction unitcomprising a combiner to combine an output signal from the switched-modeoutput stage and the error signal.
 5. A transmission device according toclaim 1, the error correction unit comprising a filter to provide afiltered transmission signal.
 6. A transmission device according toclaim 5, the filter being disposed as Band Pass Filter.
 7. A modulatorfor modulating a useful signal into a modulated signal comprising: aPulse Width Modulator (PWM) that receives a signal and that provides apulse stream signal derived from the signal; a Phase Modulator thatreceives a second signal and that provides an Local Oscillator (LO)signal; a first mixer that receives the pulse stream signal and the LOsignal and that provides an intermediate signal; a first output stagethat receives the intermediate signal and that provides an outputsignal; an error estimation block that receives the pulse stream signalprovides a first intermediate error signal; a second mixer that receivesthe first intermediate error signal and the LO signal and provides asecond intermediate error signal; a second output stage that receivesthe second intermediate error signal and that provides an error signal;a combiner that receives the output signal and the error signal and thatprovides the modulated signal.
 8. A modulator according to claim 7: theerror estimation unit comprising a filter to derive an error componentof the pulse stream signal.
 9. A modulator according to claim 7: thefirst output stage comprising at least one switched amplifier.
 10. Amodulator according to claim 7: the second output stage comprising atleast one linear amplifier.
 11. A modulator according to claim 7comprising: a Band Pass Filter to filter the modulated signal.
 12. Amethod for modulating a useful signal into a modulated signalcomprising: coding the first signal to provide a pulse stream signal;phase modulating a second signal to provide an Local Oscillator (LO)signal; mixing the pulse stream signal and the LO signal to provide anintermediate signal; amplifying the intermediate signal to provide anoutput signal; filtering the pulse stream signal to provide a firstintermediate error signal; mixing the first intermediate error signalwith the LO signal to provide a second intermediate error signal;amplifying the second intermediate error signal to provide an errorsignal; and combining the error signal with the output signal to providea modulated signal.
 13. A method according to claim 12 wherein:amplifying the intermediate signal involves use of switchedamplification.
 14. A method according to claim 12 wherein: amplifyingthe second intermediate error signal involves use of linearamplification.
 15. A method according to claim 12 comprising: Band PassFiltering of the modulated signal.
 16. An apparatus, comprising: a firstPulse Width Modulator (PWM) to receive a first input signal and providea first pulse stream signal; a second PWM to receive a second inputsignal and provide a second pulse stream signal; a first filter toreceive the first pulse stream signal and provide a first intermediateerror signal; a second filter to receive the second pulse stream signaland provide a second intermediate error signal; an adder to combine thefirst and second intermediate error signals to provide a combined errorsignal; at least one amplifier to amplify, respectively, mixed first andsecond pulse stream signals to provide first and second output signals;and a combiner to receive the combined error signal and the first andsecond output signals and to provide a transmission signal.
 17. Theapparatus according to claim 16, wherein the first input signal is anInphase component signal and the second input signal is a Quadraturecomponent signal.
 18. The apparatus according to claim 16, wherein thefirst output signal is an Inphase output signal and the second outputsignal is a Quadrature output signal.